Abstract

The antiplatelet drug clopidogrel is metabolized to an acyl-β-D-glucuronide, which causes time-dependent inactivation of CYP2C8. Our aim was to characterize the UDP-glucuronosyltransferase (UGT) enzymes that are responsible for the formation of clopidogrel acyl-β-D-glucuronide. Kinetic analyses and targeted inhibition experiments were performed using pooled human liver and intestine microsomes (HLM and HIM, respectively) and selected human recombinant UGTs based on preliminary screening. The effects of relevant UGT polymorphisms on the pharmacokinetics of clopidogrel were evaluated in 106 healthy volunteers. UGT2B7 and UGT2B17 exhibited the highest clopidogrel carboxylic acid glucuronidation activities, with a CL_int,u of 2.42 and 2.82 µL∙min^-1·mg^-1, respectively. Of other enzymes displaying activity (UGT1A3, UGT1A9, UGT1A10-H and UGT2B4), UGT2B4 (CL_int,u 0.51 µL∙min^-1·mg^-1) was estimated to contribute significantly to the hepatic clearance. Nonselective UGT2B inhibitors strongly inhibited clopidogrel acyl-β-D-glucuronide formation in HLM and HIM. The UGT2B17 inhibitor imatinib and the UGT2B7 and UGT1A9 inhibitor mefenamic acid inhibited clopidogrel carboxylic acid glucuronidation in HIM and HLM, respectively. Incubation of clopidogrel carboxylic acid in HLM with UDPGA and NADPH resulted in strong inhibition of CYP2C8 activity. In healthy volunteers, UGT2B17*2 deletion allele was associated with a 10% decrease per copy in the plasma clopidogrel acyl-β-D-glucuronide to clopidogrel carboxylic acid AUC0-4 ratio (P<0.05). To conclude, clopidogrel carboxylic acid is mainly metabolized by UGT2B7 and UGT2B4 in the liver, and by UGT2B17 in the small intestinal wall. The formation of clopidogrel acyl-β-D-glucuronide is impaired in carriers of the UGT2B17 deletion. The findings may have implications regarding intracellular mechanisms leading to CYP2C8 inactivation by clopidogrel.